The present invention relates to exposure systems for copying machines, of a particular type in which relative movement is effected between the projection system of the exposure system and the original in a predetermined direction, so that the projection system projects images of successive transverse strip-shaped sections of the original onto the recording medium. In the type of system in question, the projection system comprises a plurality of lens-row systems. Each lens row system comprises a first lens row, the lenses of which project light from a strip-shaped section of the original into an intermediate image plane; and a second lens row, the lenses of which receive light from the intermediate plane and project an image of the strip-shaped section onto the recording medium. The individual lens-row systems are spaced apart from one another in the direction transverse to the direction of elongation of the lens rows.
A system of this type, in which the image components projected by the individual lens groups combine to form a whole image, is disclosed in commonly owned U.S. Pat. No. 3,592,542. In order to increase the efficiency of illumination, the image components projected onto the recording medium can be made to directly adjoin or even somewhat overlap, both in direction transverse to the direction of relative movement as well as in the direction of relative movement. U.S. Pat. No. 3,655,284 discloses the use of a plurality of lens-row systems spaced apart in the direction of relative movement between the projection system and the original. Because plural lens-row systems are employed, each point of the recording medium is exposed more than once during travel of the recording medium through the exposure system. This multiple exposing of each point of the recording medium creates the possibility of shorter exposure times and therefore higher operating speed. Also, this multiple exposing inherently tends to equalize out differences which may exist as between the illumination effected by each lens-row system individually. This will in particular be the case when the constituent lens elements of one lens-row system are offset relative to those of the other lens-row system(s) in such a manner that, considered in the aforementioned direction of relative movement, the lens elements of one system fill the spaces between those of an adjoining system.
These advantages of plural lens-row systems are somewhat offset by practical difficulties which they inherently create. A single strip-shaped section of the original is imaged onto a corresponding strip-shaped section of the recording medium not once, but rather once by each lens-row system in turn, at successive times. If the relative movements in question, for example of original and recording medium, are not perfectly uniform and synchronized, but instead for example exhibit a certain amount of oscillation, each single strip-shaped section of the original is imaged plural times onto non-congruent strip-shaped sections of the recording medium. As a result, contours in the image being projected will be reproduced as multiple or ghost contours. Multiple contours are more easily perceived and annoying than even low-contrast or fuzzy contours of the type that can arise with a purely single exposure of comparably long effective duration. Therefore, the use of plural lens-row systems has come to necessitate, as a practical matter, the use of more expensive and fine synchronization of relative movements of originals and recording media, more expensive than would be needed for conventional objectives of the type which project a solid strip-shaped image.